1. Field of Invention
The present invention generally relates to the field of RFID communication systems, and more particularly, to a system and method for detecting an object within an RFID communication system.
2. Description of Related Art
In, for example, retail establishments, it is desirable to know whether objects or persons are passing through portals or close to portals being monitored by RFID transceivers. For example, it is desirable to know whether an object or person is present in the region of an entrance or exit of a retail establishment, and whether an object or person is present in the region of any opening or openings between a frontstore and a backstore where inventory is stored. Additionally, it is desirable to know whether an object or person is present in the region of any loading docks, or other types of portals for bringing inventory into or out of the retail establishment. Furthermore, it is desirable to know whether an object or person is in motion toward or away from any of the forgoing regions, even if the object or person is not in the immediate region.
It was known in the prior art to use infrared sources and detectors for monitoring the foregoing regions. Infrared detectors used in this manner could detect the motion of an object or person moving either toward or away from a portal. The infrared detectors could provide a detection signal when the motion was detected. Additionally, it was known to use a detection signal from an infrared detector to activate a radar transmission in order to permit further monitoring of the region. The doppler shifts of the radar transmission could then provide further information on the motion in the vicinity of the portal being monitored. Additionally, it was common to use well known light barrier devices to monitor the vicinity of portals. The light barriers could provide a detection signal when an object or person passing through the portal broke a light beam.
However, the known methods for detecting motion around the RFID transceivers required that a specialized, dedicated device be added to the RFID transceivers. Even the addition of a simple detection device such as an infrared detector or a light barrier added some size and cost to the RFID transceivers. The requirement for additional space for monitoring regions such as the regions around portals is especially problematic in retail applications that have limited and very expensive retail space.
For example, U.S. Pat. No. 7,023,341 B2 issued to Stilp teaches an RFID reader for detecting motion using doppler in a security network. The RFID reader sent and received RF signals, and measured the reflected pulses relative to the transmitted pulses. Many doppler systems like the one taught by Stilp could easily detect a person walking at a normal speed. The system disclosed by Stilp could also alter the power of its doppler transmissions. By varying the transmission power, the detection range of the RFID readers could be varied. The doppler motion detection in Stilp was performed simultaneously with searching for transponders using conventional tag interrogation techniques.
U.S. Patent Pub. No. 2008/0318684 A1 by Rofougaran teaches RF position locating in a video gaming system. The teachings in Rofougaran include sweeping an area with RF signals of several different frequency bands, and determining the physical layout of the environment based on reflected, absorbed and refracted signals, angle of incidence and backscatter of the swept signals. The distance to the player, the other objects in the room, the ceiling, the floor, the walls, etc. were determined from the received signals and stored for use during a game. Monitoring of the movements of the player thereafter during the game depended on the player wearing a gaming object.
U.S. Patent Pub. No. US2008/0001735 A1 by Tran is of general interest for teaching determining when a person passes through a door using a combination of different devices. Tran teaches using radar doppler shift of an RF signal reflected off the person. Tran also teaches using ultrasonic devices and photosensors. The results of the determinations made using the different devices could be combined to distinguish ranges.
U.S. Pat. No. 5,030,941 issued to Lizzi also teaches a number of different auxiliary detectors for detecting motion near or through RFID portals. The use of photoelectric sensors, body heat sensors and floor switches are taught by Lizzi.
However, the use of the auxiliary sensors taught by Lizzi, as well as the other systems set forth above, all require a specialized, dedicated device to be added to the RFID transceivers in order to detect the presence or motion of objects or persons in the vicinity of a RFID transceiver monitoring a portal. This increases the size and costs of the RFID transceiver.
All references cited herein are incorporated herein by reference in their entireties.